Remove the weak dictionary that maps tab objects to it markers

tools/telemetry/telemetry/core/web_contents.py

Index: tools/telemetry/telemetry/core/web_contents.py
diff --git a/tools/telemetry/telemetry/core/web_contents.py b/tools/telemetry/telemetry/core/web_contents.py
index 0b3594b259f487400341173cc9ccc6e35de240e0..c5137679de7a383edfe192a8c4eb1089f242cba7 100644
--- a/tools/telemetry/telemetry/core/web_contents.py
+++ b/tools/telemetry/telemetry/core/web_contents.py
@@ -20,6 +20,11 @@ class WebContents(object):
         'network_quiescence.js')) as f:
       self._quiescence_js = f.read()
 
+  @property
+  def id(self):
+    """Return the unique id string for this tab object."""
+    return self._inspector_backend.id
+
   def WaitForDocumentReadyStateToBeComplete(self,
       timeout=DEFAULT_WEB_CONTENTS_TIMEOUT):
     self.WaitForJavaScriptExpression(